help with diagnosis vhsb 34mm aprilia rs 125 carb problem

any ideas ? am fitting a 34 mm with a piper cone and a 162 main jet needle notch is on the second from the top notch and the mix screw is 2.5 turns out yet its spluttering up to 5000 rpm <in the low rev range> above 5 is fine pulls like a train am stumped, ive tried a selection of main jets yet to no avail, am i rite in thinking it could be a oversized pilot jet ?
cheers

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

could be mate,sounds like its floodin itself at low rpm..or try movin needle to the top notch

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

main jet will only affect full throtle and higher rpms,hence ur bike is runnin fine above 5.Try winding ur mixure screw in .start by windind all the way in then wind it out to 1 3/4 turns.put ur need on the highest clip. Try that,if worse put needle clip on the other end.these should give u an idea of witch way the set up needs to be.From there its just ifne tuning :thumbsup: good luck

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

rite orde a b34 pilot jet it came today the bike sounds crisper in the exhaust note at low rpm but the aplutters still there 4-6000 rev is unrideable ???? the needle is on the top notch already could i need a leaner / smaller needle ?
its a 34mm vhsb with
dp266 atomiser
b34 idle jet
60 choke jet
162 main jet
k57 needle
any help apreciated as im close to tearing my hair out lols

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

Are you on full throttle accelerating or part throttle when it's missing between 4-6K, If your on full throttle the needle is already in upermost position, albeit right or wrong, if your only on part throttle the needle could be sitting to low in the tube restricting fuel flow to much, so you could try raising it a notch or 3. I don't know what standard dia carb yours is but if you've gone bigger that will reduce air flow rate and mess mid range fueling when opening the throttle. Pilot jets only really effect idle and just past, maybe up to 2k revs tops. What is standard main jet size? I don't get why you put the needle in top notch, if your trying to richen it up it needs to be raised not lowered.

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

get rid of the cone filter. try it with standard airbox with the correct mount fitment

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

what falcon just said, 2 strokes rely on airbox pressures aswell, which is prob why its running shit below 6k, 2 strokes only really run with no airbox if its a race bike in which its at high rpm most of the time. why have you gone for a bigger carb anyway? the rs125 is prob as fast as its going to go with the standard carb (28mm iirc) its pointless changing, for that 0.5bhp more because no matter how much setting up your going to do it will prob never be right unless it was done by a professional imo.

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

sounds like a job for pete alton

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

cheers guys turned out to be the piper x cone back on the original air box much better thanks for all the replys
and as for y im fitting a 34 mm
the early rs 125s were sold with 34 mm dellorto carbs and had hardly any restrictions as time has gone by aprilia have decided to induce electircal, mechanical restrictions to the rs why im unsure as its a 125 and why starve it ? i think its to do with e.u regulations, im just after getting as much power as i can with out any silly cylinder modifications, the 34 mm is probably the best modification ive done so far its givin more mid range and feels quicker on the engines power band !
again thanks for all the replys

regards
steve -p-

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

the carb has a 12.5 venturi
the standard jet size for the standard bike is 155 - 160

also as for jetting the official arrow spec is this

 

Re: help with diagnosis vhsb 34mm aprilia rs 125 carb proble

Alryt mate ill try and find that std air filter and drop it down later